Latency reduction is one of the considerations in a GSM/EDGE radio access network (GERAN). Two techniques have been proposed for the latency reduction: reduced transmission time interval (RTTI) and fast acknowledgement/non-acknowledgement (ACK/NACK) reporting (FANR).
Conventionally, an ACK/NACK report is sent in an explicit message, also referred to as a radio link control/medium access control (RLC/MAC) control block. The ACK/NACK report is addressed to a particular radio resource, called a Temporary Block Flow (TBF).
A TBF is a temporal connection between a mobile station and a network to support a uni-directional transfer of data. A TBF is temporary and is maintained only for the duration of the data transfer. Each TBF is assigned a temporary flow identity (TFI) by the network. The TFI is unique among concurrent TBFs in each direction and is used instead of mobile station identity in the RLC/MAC layer. The same TFI is included in every RLC header belonging to a particular TBF.
It has been proposed to send the ACK/NACK report for a certain TBF as a “piggyback” on an RLC/MAC data block that may be addressed to another TBF. The field that carries the ACK/NACK report is referred to as a piggybacked ACK/NACK (PAN) field.
Since the PAN field is included in a data block that may be addressed to a different TBF, it is necessary to identify to which TBF the PAN field is addressed. Various proposals have been made to identify the correct TBF in the PAN field, including using a TFI or an uplink (UL) state flag (USF). During establishment of the uplink TBF, a USF is assigned to each mobile station. The USF is used by the network to indicate which mobile terminal is allowed to transmit in the following uplink radio block.
In either case, some number of bits, (typically ranging from three to five), should be dedicated to the TBF identity in the PAN field. It would be desirable to have an efficient method of sending the TBF identity in the PAN field such that no dedicated bits are needed to identify the TBF.